a detailed path-latency model for router geolocation
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A Detailed Path-latency Model for Router Geolocation
Sándor Laki*, Péter Mátray, Péter Hága,
István Csabai and Gábor Vattay
Department of Physics of Complex SystemsEötvös Loránd University
Budapest, Hungary
*E-mail: laki@complex.elte.hu
Agenda
• Introduction• Path-latency Model• Velocity of Signal Propagation in
Network• Geographic Constraints• Data Collection• Performance Analysis• Summary
Motivation
• Location information can be useful to both private and corporete users– Targeted advertising on the web– Restricted content delivery– Location-based security check– Web statistics
• Scientific applications– Measurement visualization– Network diagnostics
Geolocation in General
• Passive geolocation– Extracting location information from domain names– DNS and WhoIS databases– Commercial databases
• MaxMind, IPligence, Hexasoft– Large and geographically dispersed IP blocks can
be allocated to a single entity
• Active geolocation– Active probing– Measurement nodes with
known locations– GPS-like multilateration (CBG)
Measurement Based Geolocation
• Active measurements– Network Delays
• Delays can be transformed to geographic distance
– Round Trip Time (ping)– One-way delay
• Effects of over and underestimation
– Topology• Network-path discovery
– Traceroute with fixed port pairs
• Interface clustering– Mercator, etc.
Presentation Outline
• Introduction• Path-latency Model• Velocity of Signal Propagation in
Network• Geographic Constraints• Data Collection• Performance Analysis• Summary
Why do we need a latency model?
• The basis of active methods is to transform delays to geographic distance
• The model aims to decompose the overall packet delay to linkwise components
• Approximating propagation delays along a network pathleads to more precise distance estimations...
Modelling Packet Delays
• A packet delay (d) can be divided into…– Queuing delay (Dq)
– Processing delay (Dpc)
– Transmission delay (Dtr)
– Propagation delay (Dpg)• A given path:
• The overall packet delay for a network path (s=n0 and d=nH):
n0 n1 n2 nH…
Only the propagation component has role in the
geolocation
How to Estimate Propagation Delays
• Assumptions in the model– No queuing (Dq = 0)– The per-hop processing and transmission delays can be
approximated by a global constant (dh)• dh = Dpc + Dtr
– Based on the literature and our observations:» dh = 100s
The one-way propagation delay along a given path:
An Extra Cost - ICMP Generation Time
• In case of ICMP based RTT measurements an extra delay appears at the target node– ICMP Echo Reply Generation Time (Dg)
• The overall Round Trip Delay:
Is it possible to measure this Dg delay component?
Yes, there’s a way…
ICMP Generation Times
Less than 1%
Dg = 300 sto avoid distance underestimation
Presentation outline
• Introduction• Path-latency Model• Velocity of Signal Propagation in
Network• Geographic Constraints• Data Collection• Performance Analysis• Summary
Distance Approximation
• An upper approximation of geographical distance from source s to destination d:
• where r is the velocity of signal propagation in network [in c units]
s
d
Network cables not running
straight due to several reasons
Physical properties of the network
cables
Signal Propagation in Network
The maximum velocity we measured in
network was 0.47!
The velocity of signal
propagation in a copper cable is ~0.66-0.7!
And the average value was 0.27
The maximum value was used to
avoid distance underestimation
Presentation outline
• Introduction• Path-latency Model• Velocity of Signal Propagation in
Network• Geographic Constraints• Data Collection• Performance Analysis• Summary
Solving Geolocation
• Defining geographic constraints• We are looking for a location set where all
the constrains come true• Defining the overall tension in the system
– A cost function• By minimizing this function the problem
can be solved
» Non-convex optimization problem» Well known solutions in sensor networks
Round-Trip Time Constraint
• Using path-latency model– Round-trip propagation delay from a landmark
• Upper approximation of one-way propagation delay
L
t
The nodeto be localized
Landmark with known location
One-way Delay Constraint
• A novel constraint for a network path between two landmarks– Limiting the geographic length of a given network
path• High-precision
OWD measurements
L1 n1
L2n2
n3
Presentation outline
• Introduction• Path-latency Model• Velocity of Signal Propagation in
Network• Geographic Constraints• Data Collection• Performance Analysis• Summary
An Award-winning Testbed
• European Traffic Observatory Measurement InfrastruCture (etomic) was created in 2004-05 within the Evergrow Integrated Project.
• Open and public testbed for researchers experimenting the Internet
• 18 GPS synchronized active probing nodes• Equiped with Endace DAG cards
– High-precision end-to-end measurements• Scheduled experiments
• NO SLICES» You own the resources
during the experimentation
www.etomic.org
Best Testbed Award
Presentation outline
• Introduction• Path-latency Model• Velocity of Signal Propagation in
Network• Geographic Constraints• Data Collection• Performance Analysis• Summary
Performance Analysis
Geo-RMean error: 305 kmMax. error: 878 km
StdDev: 236 km
Geo-RhMean error: 251 kmMax. error: 699 km
StdDev: 205 km
Geo-RhOLMean error: 149 kmMax. error: 312 km
StdDev: 104 km
Presentation outline
• Introduction• Path-latency Model• Velocity of Signal Propagation in
Network• Geographic Constraints• Data Collection• Performance Analysis• Summary
Summary
• Estimating propagation delays more precisely– Separation of propagation and per-hop delays in the overall
packet latency• Velocity of signal propagation in network is much smaller
than we assumed before due to curvatures• The novel one-way delay constraints improve the accuracy
of router geolocation significantly– Nowadays these measurements are available in a few NGN
testbeds (ETOMIC, new OneLab-2 nodes, etc.)
• Plans for future extensions• The method can be combined with passive
techniques• Improving latency model
OneLab2 - The Next Generation of ETOMIC
ETOMIC
www.etomic.org
OneLab2
www.onelab.eu
www.etomic.org
OneLab2 sites:• ≥2 PlanetLab
nodes• New features
• Dummybox• WiFi access• UMTS,
WiMax…• 1 ETOMIC2-
COMO integrated node
• High precision e2e measurements
• ARGOS meas. card• available via
ETOMIC’s CMS• 1 APE box• A lightweight
measurement tool
Thank you for your attention!
Contact: laki@complex.elte.hu
This work was partially supported by the National Office for Research and Technology (NAP 2005/ KCKHA005) and the EU ICT OneLab2 Integrated Project
(Grant agreement No.224263).
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